in the games they're just disposable type, stat, and move pools that get switched out or binned indefinitely and your static team at the end is a bunch of stuff you caught in the last fifth of the game or less.
That's on you, Pokemon games are generally pretty easy and you can beat them with most any party. I beat gold with pretty much just my feraligator because I was a dumb kid who didn't level anyone else.
It's 100% a "u mad bro?" thing. They do it because they think it pisses Xi off.